The structures of polyoma virus and its polymorphic aggregates, SV40 virus, myosin subfragment-1, and the chloroplast cytochrome b6/f complex will be studied by electron microscopy and image analysis methods. These studies are aimed at answering questions about the overall structure, assembly, stability, and function of these macromolecular aggregates. We will learn about protein-protein interactions in polyoma, SV40, myosin subfragment-1, and cytochrome b6/f, protein-nucleic acid associations in polyoma and SV40, and protein-lipid associations in cytochrome b6/f. The biological significance of each of these systems is well documented. Polyoma and SV40 do not cause malignancies in their natural hosts (mice and rhesus monkeys), but their oncogenic potential is revealed when high concentrations of virus are injected into either foreign hosts or natural hosts lacking a functional immunological system. Subfragment-1, the head portion of myosin, is responsible for force generation in muscle through the hydrolysis of ATP and interaction with actin. Cytochrome b6/f, an integral membrane-spanning complex in chloroplast thylakoids, is involved in photosynthetic and respiratory energy transduction. The potential to study these and similar structures requires continued efforts to develop and implement new techniques of electron microscopy and image analysis as well as the application of established procedures. Microscopy of frozen-hydrated specimens will help reveal the "native" structure of biological molecules, and implementation of highly interactive, computer graphics image analysis routines will allow flexible and efficient processing of micrographs from a greater variety of biological systems of increased complexity.